Tech Roll Call: M-I SWACO won the prestigious International Platinum Award for the innovative Shell Dunlin Attic Oil Recovery project
The Production Technologies group, under Charles Benson, worldwide business development manager for Production Technologies, won the prestigious International Platinum Award at the Energy Institute Awards held in London on Nov. 19, 2008. The award recognized the innovative technology developed to safely extract oil trapped in the attic space of the subsea storage cells in the Dunlin oilfield 150 mi (242 km) northeast of Lerwick, Shetland, and 311 mi (500 km) northeast of Aberdeen, Scotland. Recovery of the over 1.5 million barrels of fluid from 75 subsea cells 500 ft (150 m) below the surface was a critical step to complete decommissioning of the platform. Oil trapped in the cells represented significant HSE risk in terms of leg entry and loss of containment to the sea.
“The award acknowledges the success and endorses our commitment and ability to engineer solutions for the decommissioning market at a time when many operators are preparing their plants for cessation of aging assets,” said Benson.
A world’s first, and the result of three years of intensive work, the Shell Dunlin Attic Oil Recovery project was unprecedented in its scale and complexity in the North Sea. It involved in situ gas generation within the cell structure of the North Sea installation. The aim of the project was to safely free the four cell groups of the remaining 1.5 million barrels of liquids, including 250,000 barrels of oil.
The patented technology involves in situ generation of inert gas to displace the crude oil layer to the level of the export pipe for recovery. The system was developed in stages, starting with a small-scale 2-cell model. Next, a 20-cell matrix of interconnected, hand-blown glass cells was tested. Field application was validated using a large, 1:25 scale, acrylic glass model before optimizing the design using a 20-cell pressurized steel model.
Full-scale implementation began in late 2006. PLONAR-rated acid and alkali solutions, mixed on the fly, were injected into the cells using a static in-line mixer at the entry point of the cell, directly from the back of a dedicated PSV, via two independent, dry-break umbilical lines. The gas generated in the cell displaced the oil down to the import/export line, allowing rig pumps to recover the oil. Cell leakage was prevented using sized wax particles suspended in a gel. Deployed ahead of the gas generation phase, the particles gravitated through the oil to form a seal on the inner surface of the cell.
Following complete oil recovery, the gas cap was absorbed using a gas scavenging system—a mixture of base CO2 scavenger, a brine hydroxide salt inhibitor and an alcohol density modifier—leaving the cells full of seawater.
The successful application required the development of a logistic and engineering solution to address the challenges of manufacture, storage and delivery of the quantities of chemicals required. The nine-month time-critical operation included the manufacture and storage of 20,000 tons of chemicals in Teeside, UK, over 700 road tanker journeys and eight fully laden PSV sailings. All of this was accomplished during some of the worst weather conditions ever experienced in a region known for bad weather. Through the process, the risk of failure to deliver the technology was managed through close cooperation across the multidisciplinary team including Shell, DOF, Qserv, Stats, Aubin, Univar, Hutchinson, Ineos, LV Shipping and PD Ports.
The project was so successful that instead of being decommissioned, Dunlin has been sold to a new independent North Sea operator, thus extending the life of the platform by many years.
The technology developed by M-I SWACO, now proven in one of the world’s most difficult environments, will have significant application in the future, not only in the North Sea but worldwide.
The EI Awards, in partnership with Deloitte, acknowledge the contribution that energy professionals make on a daily basis and whose achievements stretch the boundaries of excellence and commitment to their work. Previous winners of the International Platinum Award include Shell for the Brent Alpha redevelopment, ExxonMobil for the Link school program and Nexen for the Buzzard project.
